gistfile1.py

class Event(object):

    def __init__(self):
        self.subscribers = []

    def subscribe(self, callback):
        self.subscribers.append(callback)

    def notify(self, *args, **kwargs):
        for subscriber in self.subscribers:
            subscriber(*args, **kwargs)


class Entity(object):

    def __init__(self):
        self.died_event = Event()

    def kill(self, other):
        print "killing!!! hahaha"
        other.die()

    def die(self):
        print "omg I'm dying!!"
        self.died_event.notify(self)


class Game(object):

    def __init__(self):
        self.entities = []

    def create_entity(self):
        entity = Entity()
        entity.died_event.subscribe(self.on_entity_death)
        self.entities.append(entity)
        return entity

    def on_entity_death(self, entity):
        print "I'm being notified that my poor entity died... :("
        self.entities.remove(entity)
        
        
if __name__ == "__main__":
    game = Game()
    entity1 = game.create_entity()
    entity2 = game.create_entity()
    entity1.kill(entity2)